全文获取类型
收费全文 | 182310篇 |
免费 | 3427篇 |
国内免费 | 1551篇 |
专业分类
化学 | 87998篇 |
晶体学 | 2114篇 |
力学 | 7130篇 |
综合类 | 54篇 |
数学 | 16290篇 |
物理学 | 51481篇 |
无线电 | 22221篇 |
出版年
2021年 | 1413篇 |
2020年 | 1598篇 |
2019年 | 1618篇 |
2018年 | 1898篇 |
2017年 | 1890篇 |
2016年 | 3070篇 |
2015年 | 2140篇 |
2014年 | 3203篇 |
2013年 | 7444篇 |
2012年 | 6091篇 |
2011年 | 7490篇 |
2010年 | 5298篇 |
2009年 | 5535篇 |
2008年 | 7161篇 |
2007年 | 7253篇 |
2006年 | 6874篇 |
2005年 | 6351篇 |
2004年 | 5698篇 |
2003年 | 4969篇 |
2002年 | 4979篇 |
2001年 | 5389篇 |
2000年 | 4250篇 |
1999年 | 3503篇 |
1998年 | 3136篇 |
1997年 | 3079篇 |
1996年 | 2772篇 |
1995年 | 2629篇 |
1994年 | 2602篇 |
1993年 | 2344篇 |
1992年 | 2557篇 |
1991年 | 2662篇 |
1990年 | 2428篇 |
1989年 | 2393篇 |
1988年 | 2299篇 |
1987年 | 1963篇 |
1986年 | 1930篇 |
1985年 | 2413篇 |
1984年 | 2513篇 |
1983年 | 2103篇 |
1982年 | 2242篇 |
1981年 | 2135篇 |
1980年 | 2061篇 |
1979年 | 2161篇 |
1978年 | 2326篇 |
1977年 | 2193篇 |
1976年 | 2239篇 |
1975年 | 2124篇 |
1974年 | 2168篇 |
1973年 | 2162篇 |
1972年 | 1438篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
991.
F. Kulcsár D. Teherani H. Altmann 《Journal of Radioanalytical and Nuclear Chemistry》1982,68(1-2):161-168
It is pessible to study experimentally Cherenkov light spectra in a liquid scintillation spectrometer with colour filters.
Cherenkov light spectra of60Co,198Au,115Cd,143Ce,140La,32P,86Rb,76As,42K and an external standard were studied in a Packard 3375 type liquid scintillation spectrometer, using 11 various Kodak Wratten
filters. The absorption maxima of the filters ware in the 410–796 nm interval. 相似文献
992.
The interaction of three forward beams in a BSO crystal is investigated under conditions when the two pump beams are anti-symmetrically detuned and the signal beam is phase modulated. For sinusoidal phase modulation the signal gain is shown to be dependent on the instantaneous frequency detuning. Single and double maxima in gain are obtained depending on the voltage amplitude applied to the piezoelectric mirror. For triangular phase modulation a slight asymmetry is found in the gain versus detuning curve. 相似文献
993.
994.
W. Potzel J. Moser Ulrike Potzel F. J. Litterst G. M. Kalvius J. Gal M. Boge J. Chappert J. Spirlet 《Hyperfine Interactions》1987,34(1-4):391-405
Due to the wider radial extent of 5f electrons when compared to their 4f counterparts, intermetallics of the light actinides show a broad spectrum of magnetic properties ranging from the localized magnetism of the lanthanides to the itinerant magnetism often found in transition metal compounds. One parameter which strongly influences the magnetic character of the compound is the actinide-actinide separation which can experimentally be varied by the application of high pressure. The question of 5f electron delocalization will be reviewed with respect to Moesshauer high pressure data on NpCo2si2, NpAl2, NpOs2 and new results will be presented of NpAs. The connection of hyperfine parameters with results of X-ray diffraction studies will be discussed.Work supported by the Bundesministerium für Forschung und Technologie, Federal Republic of Germany 相似文献
995.
We introduce a general scheme to realize perfect storage of quantum information in systems of interacting qubits. This novel approach is based on global external controls of the Hamiltonian that yield time-periodic inversions in the dynamical evolution allowing a perfect periodic quantum state reconstruction. We illustrate the method in the particularly interesting and simple case of spin systems affected by XY residual interactions with or without static imperfections. The global control is achieved by step time inversions of an overall topological phase of the Aharonov-Bohm type. Such a scheme holds both at finite size and in the thermodynamic limit, thus enabling the massive storage of arbitrarily large numbers of local states, and is stable against several realistic sources of noise and imperfections. 相似文献
996.
Application of graph-theoretic methods to new perimeter polynomials for connected clusters on a lattice yields extra data on the total number of clusters and for the coefficients in the series expansion for the mean size of clusters at low densities. The lattices studied are the square, the square with next nearest neighbors, the triangular, and the simple cubic. 相似文献
997.
998.
E. N. Abdullin N. G. Ivanov B. M. Kovalchuk I. N. Konovalov V. F. Losev A. N. Panchenko Yu. N. Panchenko V. S. Skakun V. F. Tarasenko A. G. Yastremsky 《Laser Physics》2006,16(1):104-115
Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the
output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results
on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns,
a divergence of 0.01 mrad, a spectral line width of 0.01 cm−1, and a pulse energy of up to 330 J are obtained.
Original Text ? Astro, Ltd., 2006. 相似文献
999.
J. Jiang B.Y. Jiang C.X. Ren F.M. Zhang T. Feng X. Wang X.H. Liu S.C. Zou 《Applied Surface Science》2006,252(10):3642-3646
Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO3 compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested. 相似文献
1000.
F. García 《Topology and its Applications》2006,153(15):2886-2892
In this paper we characterize the class of uniform Eberlein compact spaces through a network condition and also in terms of covering properties for the square of the space. 相似文献